Verformungsverhalten künstlicher Makroporen unter variierenden Druck- und Bodenfeuchtebedingungen

In the present study, the stability and defomation behavior of artificial macropores under varying load and soil moisture levels was investigated b. means of X-ray computed tomography (CT). The results should be a reference for similar studies on soil samples from field trials. The soil tested was a well structured humic silt loam with a bulk density of 1 g cm^-3. Round-shaped pores of vertical and 45 degree angle orientation were drilled into the samples with a plastic needle (∅ 5 mm). These samples were compacted in an uniaxial compression device at four different moisture level and four pressure stages each. Stepwise CT imaging and its 3-dimensional reconstruction enabled us to study systematically the mode and intensity of pore deformation. As a result four different deformation stages could be identified in dependence from load, soil moisture, and pore orientation. The deformation stage "stable" was characterized by mostly unaffected pore dimensions and shapes. Increasing load and/or moisture content led to prominent bottle necks within the pores which was named "structure deformation". Due to the shape and size of these bottle necks it seems to be most likely that still intact aggregates were moved into the inner pore space, reducing the mean cross sectional areas. The deformation stage "total deformation" appeared with further increase of load and/or moisture. The aggregated structure disappeared while the inner roughness of the pores became smoother again. This represents a viscoplastic deformation. Cross sectional areas, pore lenghts, and volumes significantly decreased. The stage "extinction" was finally reached at water contents around the liquid limit, where the pore structure was completely lost, at least on CT resolution level. The deformation stages could be attributed to load stages depending from pore orientation. Unexpectedly, all pores kept their originally round shape over all stages until extinction.